Piston air compressors are used in the form of, for example, single-cylinder piston compressors in pneumatic systems of heavy motor trucks. A piston air compressor of the general type under consideration has a piston that runs in a cylinder. During its travel from a bottom dead point to a top dead point, the piston compresses air, which then emerges from the piston air compressor as compressed air through a diaphragm valve functioning as a check valve. The compressed air is passed via a pressure line into an air-conditioning system, which dries the compressed air and passes it further via a control valve to consuming loads, such as a compressed-air tank.
If the compressed-air tank is completely filled, the piston air compressor is switched to idling. In this way the pressure line remains under pressure. At the same time, a connection chamber in the single-cylinder piston air compressor is connected. During its travel from the bottom dead point to the top dead point, the piston compresses the air in the connection chamber, and the compressed air forces the piston to travel back from the top dead point to the bottom dead point so that no energy other than flow losses has to be expended during idling. The maximum peak pressure that can be developed is inversely proportional to the volume of the connection chamber. As an example, if the connection chamber is precisely as large as the displacement volume, the peak pressure when the piston is at the top dead point corresponds to twice the minimum pressure when the piston is at the bottom dead point.
In two-piston or multi-piston compressors, individual cylinders are in communication with one another via a connection chamber during idling such that substantially no energy is needed. A disadvantage of such piston air compressors is that the diaphragm valve used as a check valve has a certain leakage flow, which is expressed in liters per minute and is also known as “looseness.” Because of the looseness, compressed air from the pressure line can flow into the cylinders of the piston air compressor. Thus, high pressures are reached during compression. Because of these high pressures, compressed air flows along between the cylinder and piston and thus arrives in the compressor housing, in which oil lubrication of the piston compressor also takes place. For environmental reasons, with heavy motor trucks, this air must be passed through the internal combustion engine in order to avoid polluting the environment with air containing lubricating oil. If the internal combustion engine of the heavy motor truck is equipped with a turbocharger, however, the air containing lubricating oil may lead to accelerated aging of the turbocharger.